Green polyaniline hydrochloride film was converted to a blue polyaniline base and exposed to an ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. The ionic liquid was found to interact with polyaniline base in similar manner like an acid, and the green colour corresponding to conducting form was recovered. The resulting material maintained its “salt” character even above 200 °C, while the deprotonation of standard polyaniline hydrochloride took place under similar conditions. The state and the changes in molecular structure have been assessed by UV-visible and FTIR spectra. The experiments demonstrate a strong interaction between polyaniline and ionic liquid, which results in the conductivity and improved thermal stability of resulting material.